Galaxies such as our Milky Way have their own large-scale magnetic fields. Although these fields are weak compared to planetary fields, scientists think the galactic versions help establish rates of star formation, guide cosmic rays, and regulate the dynamics of interstellar gas.

Based on Fermi's data, "we've found that these weak magnetic fields should be everywhere. They should be outside the galaxies, filling the whole universe, even where there are no galaxies, no clusters, no anything," said study co-author Andrii Neronov of the University of Geneva's ISDC Centre for Astrophysics in Switzerland.

Since the new findings suggest magnetic fields can form outside galaxies, "perhaps those magnetic fields were created before the galaxies were formed," Neronov said.

Sowing the Seeds for Galactic Fields

According to the theory, primordial seed fields could have been created from charged particles spit out during violent events such as supernovae.

But other seed fields would remain roaming through intergalactic space—and that's what Neronov and colleagues think they've found.

More precisely, the team saw a lack of very high-energy gamma rays in Fermi data on blazars, galaxies with supermassive black holes at their centers that spew jets of particles at near the speed of light.

The gamma rays that reach Earth from blazars should be at a certain energy level. But the gamma rays Neronov's team saw appear to have been sapped of some of their strength, which is exactly what would have happened if the gamma rays had interacted with weak magnetic fields along the way.

"What we've detected could be this initial weak field, and that could resolve the problem of the origin of [modern] magnetic fields in the Milky Way and other galaxies, because we may now know the initial conditions," Neronov said.

Magnetic Mysteries Remain

The scientists aren't sure which high-energy processes might have created the very first magnetic fields in a young, galaxy-less universe, although there's no shortage of candidates.